Temperature-dependent switch comprising a spacer ring

Abstract

A temperature-dependent switch has a temperature-dependent switching mechanism arranged in a housing having an upper part and a lower part. A first contact area is arranged on an inner side of the upper part and a second contact area is arranged internally in the lower part. The switching mechanism comprises a current transfer element, a bimetallic snap-action disc and a movable contact area. The moveable contact area is connected to the current transfer element and interacts with the first contact area, the bimetallic snap-action disc lifting off the movable contact area from the first contact area depending on the temperature of the bimetallic snap-action disc. A resistance ring is arranged between the upper part and the lower part and is electrically in series with the current transfer element between the first and second contact areas when the switch is in its closed state.

Claims

1. A temperature-dependent switch having a closed state, said switch comprising: a temperature-dependent switching mechanism, said switching mechanism comprises a current transfer element, a bimetallic snap-action disc and a movable contact area connected to the current transfer element, a housing accommodating the switching mechanism and comprising an upper part with an inner side and a lower part, a resistance ring being arranged between said upper part and said lower part, a first contact area being provided on said inner side of said upper part, a second contact area being provided internally in the lower part, the switching mechanism producing, in temperature-dependent fashion, an electrically conductive connection between the first and second contact areas, said movable contact area interacting with said first contact area, the bimetallic snap-action disc lifting off the movable contact area from said first contact area depending on the temperature of said bimetallic snap-action disc, said resistance ring being arranged electrically in series with said current transfer element between said first and second contact areas when the switch is in its closed state, wherein the resistance ring comprises an upper ring area and a lower ring area, the current transfer element comprising a rim resting on the upper ring area, the lower ring area resting indirectly or directly on the second contact area, and wherein a spacer ring is arranged between said rim of said current transfer element and said upper part, said rim of said current transfer element being fixed between said spacer ring and said resistance ring.

2. The switch of claim 1, wherein the current transfer element is embodied as a spring snap-action disc.

3. The switch of claim 1, wherein the switching mechanism comprises, in addition to the current transfer element, a spring snap-action disc, which bears the movable contact area.

4. The switch of claim 3, wherein the spring snap-action disc is arranged between the current transfer element and the bimetallic snap-action disc.

5. The switch of claim 4, wherein the spring snap-action disc comprises a rim held between the resistance ring and the second contact area.

6. The switch of claim 3, wherein the spring snap-action disc has a greater electrical resistance than the series circuit comprised of the current transfer element and the resistance ring.

7. The switch of claim 3, wherein the current transfer element consists of a material that has a lower specific electrical resistance than the spring snap-action disc.

8. The switch of claim 3, wherein the current transfer element comprises a coating that improves conductivity.

9. The switch of claim 3, wherein the current transfer element comprises bent slots extending radially outwards.

10. The switch of claim 1, wherein the resistance ring is manufactured from a material having a specific electrical resistance at 20 C. which is greater than that of copper.

11. The switch of claim 1, wherein said upper ring area comprises a first section and said lower ring area comprises a second section, said first and second sections being provided with an electrically conductive coating having a lower specific electrical resistance than the material of the resistance ring.

12. The switch of claim 11, wherein the resistance ring has an ohmic resistance between the first and second sections of between 2 and 50 m.

13. The switch of claim 11, wherein at least one of the first and second sections covers less than 50% of the respective ring area.

14. The switch of claim 11, wherein the first section is circumferentially offset with respect to the second section.

15. The switch of claim 11, wherein the resistance ring has an ohmic resistance between the first and second sections of between 5 and 30 m, each of the first and second sections covers less than 35% of the respective ring area, and the first section is circumferentially offset with respect to the second section.

16. The switch of claim 11, wherein the coating comprises a silver-containing coating.

17. The switch of claim 1, wherein the resistance ring consists of a material selected from the group consisting of an iron alloy, a copper alloy, brass, bronze, constantan and stainless steel.

18. A temperature-dependent switch having a closed state, said switch comprising: a temperature-dependent switching mechanism, said switching mechanism comprises a current transfer element, a bimetallic snap-action disc and a movable contact area connected to the current transfer element, a housing accommodating the switching mechanism and comprising an upper part with an inner side and a lower part, a resistance ring being arranged between said upper part and said lower part, a first contact area being provided on said inner side of said upper part, a second contact area being provided internally in the lower part, the switching mechanism producing, in temperature-dependent fashion, an electrically conductive connection between the first and second contact areas, said movable contact area interacting with said first contact area, the bimetallic snap-action disc lifting off the movable contact area from said first contact area depending on the temperature of said bimetallic snap-action disc, said resistance ring being arranged electrically in series with said current transfer element between said first and second contact areas when the switch is in its closed state, wherein the resistance ring comprises an upper ring area and a lower ring area, the current transfer element comprising a rim resting on the upper ring area, the lower ring area resting indirectly or directly on the second contact area, and wherein said upper ring area comprises a first section and said lower ring area comprises a second section, said first and second sections being provided with an electrically conductive coating having a lower specific electrical resistance than the material of the resistance ring.

19. A resistance ring for a temperature-dependent switch, said resistance ring comprising an upper ring area and a lower ring area and being manufactured from a material that has a specific electrical resistance at 20 C. that is greater than that of copper, wherein the upper ring area comprises a first section and the lower ring area comprises a second section, said first and second sections being provided with an electrically conductive coating, which has a lower specific electrical resistance than the material of the resistance ring, and wherein the first section is circumferentially offset with respect to the second section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention are illustrated in the attached drawing and will be explained in more detail in the description below. In the drawing:

(2) FIG. 1 shows a schematic, sectional side view of a temperature-dependent switch in the closed state;

(3) FIG. 2 shows an exploded illustration of the switch shown in FIG. 1; and

(4) FIG. 3 shows the resistance ring from FIG. 2 in a schematic plan view and in section along the line A-A.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 shows a schematic side view, which is not true to scale, of a temperature-dependent switch 10 that is in its closed state and is circular in plan view and has a temperature-dependent switching mechanism 11, which is arranged in a housing 12.

(6) The housing 12 comprises an upper part 14, which closes a pot-like lower part 15.

(7) The upper part 14 bears a stationary mating contact 16, whose outer side acts as first external connection 17 for the switch 10. The lower part 15 has a base 18, whose outer side acts as a second external connection 19 for the switch 10.

(8) A first contact area 22 for the switching mechanism 11, which contact area 22 is formed on the stationary mating contact 16, is provided on an inner side 21 of the upper part 14.

(9) A peripheral shoulder 23 is arranged in the lower part 15 and acts as second contact area 24 for the switching mechanism 11.

(10) A resistance ring 25, which will be described in more detail, rests on the peripheral shoulder 23, and a spacer ring 26 is arranged on said resistance ring. An insulating film 27 rests on the spacer ring 26, with in turn the upper part 14 resting on said insulating film 27.

(11) The insulating film 27 is drawn upwards between the upper part and a raised rim 28 of the lower part 14, where it is pressed by the flanged rim 28 towards the upper part 14.

(12) Yet a further insulating film 29 is arranged on the upper part 14.

(13) In this way, the shoulder 10 is hermetically sealed, the insulating films 27 and 29 ensure that neither dust nor moisture or other impurities can enter the interior of the switch 10 between the raised rim 28 and the upper part 14.

(14) The electrically conductive upper part 14 and the electrically conductive lower part 15 are electrically insulated from one another by the insulating film 27, wherein an electrically conductive connection is produced between the first contact area 22 and the second contact area 24 by the temperature-dependent switching mechanism 10.

(15) The switching mechanism 11 comprises, for this purpose, a movable contact part 31, on which a movable contact area 32 is provided, which points towards the first contact area 22. In the closed state of the switch 10, as is shown in FIG. 1, the first contact area 22 and the movable contact area 32 bear against one another.

(16) The movable contact part 31 is mushroom-shaped in cross section, wherein a stepped holding ring 33 is positioned on the stalk, said holding ring bearing a bimetallic snap-action action disc 34, a spring snap-action disc 35 and a current transfer element 36.

(17) The bimetallic snap-action disc 34 is supported with its rim 37 internally on the base 18 of the lower part 15.

(18) The spring snap-action disc 35 lies with its rim 38 between the resistance ring 25 and a step 40 on the peripheral shoulder 23.

(19) The current transfer element 36 is clamped in with its rim 39 between the resistance ring 25 and the spacer ring 26.

(20) FIG. 2 shows the switch in an exploded illustration, from which it can be seen that the bimetallic snap-action disc 34 and the spring snap-action disc 35 are in the form of circular discs, in precisely the same way as the current transfer element 36. Alternatively, these three component parts 34, 35 and 36 can also be oval or star-shaped or cross-shaped.

(21) In the closed state of the switch 10 shown in FIG. 1, the spring snap-action disc 37 presses the movable contact part 31 against the stationary mating contact 16, with the result that the first contact area 22 and the movable contact area 32 bear mechanically against one another and are electrically conductively connected to one another.

(22) Owing to the fact that the rim 38 of the spring snap-action disc 35 is supported on the shoulder 40, the spring snap-action disc 35 is electrically conductively connected to the second contact area 24.

(23) When the switch 10 is closed as shown in FIG. 1, therefore, a first current path is formed between the stationary mating contact 16, the movable contact part 31, the spring snap-action disc 35 and the electrically conductive lower part 15.

(24) A current path formed by the current transfer element 36 and the resistance ring 25 is connected in parallel with this current path, with the result that a current divider is formed.

(25) The movable contact part 31 is namely also electrically connected to the current transfer element 36, which in turn rests with its rim 39 on the resistance ring 35, which in turn rests directly on the second contact area 24.

(26) It can be seen in particular in FIG. 2 that the current transfer element 36, the spring snap-action disc 35 and the bimetallic snap-action disc 34 each have a central bore 41, 42 and 43, respectively, which rest on the steps of the holding ring 33.

(27) While the current transfer element 36 and the spring snap-action disc 35 are clamped in electrically conductively and mechanically fixedly between the holding ring 33 and the movable contact part 31 via the openings 41 and 42 of said current transfer element and said spring snap-action disc, the bimetallic snap-action disc 34 rests with its opening 43 loosely on a lowermost step 44 of the holding ring 33.

(28) As can also be seen from FIG. 2, the current transfer element 36 is furthermore provided with bent slots 45 extending radially outwards. These slots 45 mean that the current transfer element 36 does not have a mechanical spring effect, with the result that it does not influence, or only influences unnoticeably, the temperature-dependent switching operation of the temperature-dependent switching mechanism 11.

(29) The switching mechanism 11 could alternatively also be designed in such a way that the spring snap-action disc 35 is moved to the position of the current transfer element 36, i.e. is clamped in with its rim 38 between the spacer ring 26 and the resistance ring 25. The current transfer element 36 would then be formed quasi by the spring snap-action disc 35, with the result that the switching mechanism 11 comprises the bimetallic snap-action disc 34 and a current transfer element 36, which now also takes on the function of a spring snap-action disc 35.

(30) However, in the switching mechanism 11 shown in FIG. 1, the current transfer element 36 is used substantially for conducting current because the resistance of the series circuit comprising the current transfer element 36 and the resistance ring 25 is markedly lower than the resistance of the spring snap-action disc 35.

(31) The spring snap-action disc 35 is used primarily to keep the switch closed, i.e. to exert the contact pressure with which the movable contact part 31 rests on the stationary mating contact 16.

(32) The bimetallic snap-action disc 34 rests loosely on the step 44 in the closed position of the switch 10 shown in FIG. 1, i.e. is not in operation either electrically or mechanically.

(33) If the temperature in the interior of the switch 10 increases, the temperature of the bimetallic snap-action disc 34 also increases, and the latter then moves upwards with its rim 37 and comes into bearing contact with the rim 38 of the spring snap-action disc 35. When the bimetallic snap-action disc 34 bends further, it then presses the movable contact part 31 downwards and in the process lifts off the movable contact area 32 from the first contact area 22, with the result that the switch 10 is opened.

(34) During this opening movement, arcs can be produced between the movable contact part 31 and the stationary contact 16, wherein in addition sparks may also fly.

(35) In addition, in the case of a switch which has neither a resistance ring 25 nor a current transfer element 36, sparking can also arise at the rim 38 of the spring snap-action disc 35.

(36) As already described at the outset, the arc formation and in particular the sparking can result in contact erosion being caused at the contact areas 22 and 24 and at the movable contact area 32 and the rim 38 of the spring snap-action disc 35, which in particular in the case of relatively high currents limits the life, i.e. the number of permissible switching cycles of such a switch 10.

(37) Owing to the fact that the switch 10 now has a resistance ring 25, whose resistance value is high in relation to the resistance of the current transfer element 36 and contact resistances between the contact areas 22 and 32 and the rims 38 and/or 39 of the spring snap-action disc 35 and/or the current transfer element 36, the majority of the heat in the switch 10 is now produced by the current flow through the resistance ring 25.

(38) In this way, the contact areas at the thus described contact resistances are not heated as much, which already results in the contact erosion being markedly reduced.

(39) Owing to the resistance of the resistance ring, the switch can thus also switch with a defined current dependence because the heat produced in the resistance ring 25 is conducted directly into the interior of the switch 10 and therefore towards the bimetallic snap-action disc 34.

(40) This protective function is developed by the resistance ring 25 already in the case of a switching mechanism 11 which has a spring snap-action disc 35 as current transfer element 36.

(41) However, the protective effect in the case of the embodiment shown in FIG. 1 is particularly efficient because the resistance of the spring snap-action disc 35 in relation to the resistance of the resistance ring 25 can be designed to be very high there, with the result that the majority of the operating current of the device to be protected flows through the series circuit comprising the current transfer element 36 and the resistance ring 25.

(42) The spring snap-action disc is manufactured from stainless steel, for example, and does not have a silver coating, contrary to conventional practice, with the result that it has a resistance of 150 m between its opening 42 and its rim 38.

(43) The current transfer element 36, on the other hand, is manufactured from a copper alloy, for example, and is additionally provided with a silver coating, with the result that it has a resistance of a few m between its opening 41 and its rim 39.

(44) The resistance ring 25 is designed, in a manner yet to be described, in such a way that it has a resistance of from 5 to 15 m to the current flow.

(45) During continuous operation in the applicant's rooms, such a switch has withstood more than 3000 switching cycles at an operating current of 25 amperes, i.e. has demonstrated a capacity which otherwise only switches with a very complicated design having a contact bridge demonstrate, as are known, for example, from DE 26 44 411 A1 mentioned at the outset.

(46) In other words, the spring snap-action disc has a higher electrical resistance than the series circuit comprising the current transfer element and the resistance ring.

(47) The current transfer element 36 consists namely of a material which has a lower specific electrical resistance than the spring snap-action disc, wherein the current transfer element also has a coating with improved conductivity consisting of silver.

(48) The resistance ring 25 consists of a material, in particular a metal or a metal alloy, which has a specific electrical resistance that is greater than that of copper at 20 C. The resistance ring 25 is manufactured from constantan, for example.

(49) In order now to configure the resistance ring 25 in such a way that it has a resistance of from 5 to 15 m between the rim 39 of the current transfer element 36 and the second contact area 24, said resistance ring is provided with a selective coating, as will now be explained with reference to FIG. 3.

(50) The resistance ring 25 is shown in plan view at the bottom in FIG. 3, and in section at the top in FIG. 3, along the line A-A from FIG. 3 at the bottom.

(51) The resistance ring 25 has an upper ring area 46, on which the rim 39 of the current transfer element 36 rests.

(52) In parallel therewith, the resistance ring 25 has a lower ring area 47, with which it rests directly on the second contact area 24.

(53) The resistance ring 25 is ring-shaped with an outer diameter (indicated at 48) and an inner diameter (indicated at 49). The current transfer element 26 has a thickness (indicated at 51) between the two ring areas 46 and 47.

(54) In the embodiment shown, the outer diameter 49 is approximately 10.5 mm, the inner diameter 49 is approximately 8.5 mm, and the thickness 51 is approximately 0.35 mm.

(55) Spring sheet metal which has been coated selectively has been used as the material.

(56) The upper ring area 46 is provided in a section 52 with a silver coating 53, while the lower ring area 47 is provided in a section 54 with a silver coating 55.

(57) The two sections 52 and 54 are thus arranged on different ring areas 46, 47 and are circumferentially offset with respect to each other. In the embodiment shown, the first section 52 is offset with respect to the section 54 by 180 such that the two sections 52, 54 are diametrically opposed to each other. The two sections 52 and 54 each take up approximately a third of the total area of the respective ring area 46 and 47, respectively.

(58) The operating current of a device to be protected now flows through the silver coating 53 or 55 from the rim 39 of the current transfer element 36 into the section 52 and from there so to speak longitudinally or circularly through the resistance ring 25 as far as the section 54, where the current enters the second contact area 24.

(59) The resistance value between the sections 52 and 54 can thus be varied by virtue of the sizes of said two sections 52 and 54, for which reason volume resistances between 2 and 50 m can be realized even in the case of a resistance ring 25 consisting of constantan with a thickness of only 0.35 mm.